import sequtils,strutils,strscans,algorithm,math,future,macros
template get*():string = stdin.readLine() #.strip()
let
  N = get().parseInt()
  V = get().split().map(parseInt)
var ok,no = 0
for i,v in V:
  (no,ok) = (ok + v,max(ok,no))
echo max(ok,no)